<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
   "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>week4-question</title>
<script type="text/javascript">
  function isEmpty(){
      if (document.getElementById("input").value==""){
      	alert("Please enter some data");
      	return false;
      }
      return true;
  }
</script>
</head>
<body>
<form id="name">
	  <input type="text" id="input"/>
	  <input type="submit" value="submit" onclick="return isEmpty()"/>
</form>
</body>
</html>